1. Field of the Invention
The present invention relates to a conductive actuator.
2. Description of the Background Art
An actuator realizing a small displacement by a string-shaped shape memory alloy is promising as an actuator of a small apparatus. However, since the displaceable amount of the SMA is very small, high mounting precision is demanded.
For example, in the case of applying an actuator using an SMA (SMA actuator) to a camera unit to be assembled in a portable phone having a thickness of about 10 mm, the size of the SMA actuator has to be also set to about 10 mm. Since a displaceable amount of a general SMA is about 4%, the displaceable range of the SMA is ±0.2 mm. Therefore, in the case of effectively utilizing 90% or more of the displaceable range, the mounting precision of the SMA actuator has to be set to ±0.02 mm.
Since a string-shaped SMA has flexibility, it is difficult to mount the SMA actuator with high precision. Moreover, a general Ti shape memory alloy is heat-sensitive, so that solder cannot be used for fixation. It makes more difficult to perform high-precision fixation.
To fix an SMA, conventionally, methods such as caulking, press fitting, sandwiching of the SMA between metal plates, and the like are used (for example, Japanese Patent Application Laid-Open Nos. 06-60577 (1994), 2002-98911, and 2004-76882).
However, each of the caulking, press fitting, and sandwiching of the SMA between metal plates requires a considerable force for fixation. The possibility that each of the methods exerts an adverse influence on the precision in mounting of an SMA actuator to a small apparatus is high.
For example, Japanese Patent Application Laid-Open No. 06-60577 (1994) discloses a technique using an SMA actuator as an actuator for moving a head of a magnetic recording apparatus. In the technique, a head holding plate with a spring is pulled by the SMA actuator at an acute angle, a movable amount of the head is increased by the mechanism, and both ends of the SMA actuator are attached to terminals by caulking. Such a configuration has a problem such that, when the length of the SMA actuator varies, the stress on the head holding plate fluctuates and the distance between the head and the disk surface becomes unstable. When the head is floated by air resistance as a precondition, the head holding plate has to be soft, so that the problem cannot be solved unless the length of the SMA actuator and the stress should be managed. In the technique, however, the solving method is not considered.
Japanese Patent Application Laid-Open No. 2002-98911 discloses a driving unit in which the length of the SMA actuator and the stress are adjusted. In the technique, however, an SMA actuator is formed by assembling a driving part so as to be sandwiched by the SMA actuator in a state where the SMA actuator is temporarily held. Consequently, it is feared that the SMA actuator may be deviated or deformed due to stress applied when the driving part is assembled and stress of temporary holding, and the adjusted length of the SMA actuator shifts by 0.02 mm or more. The larger the number of components is, the more an error occurs in a part size (parts tolerance), so that it is extremely difficult to realize adjustment of the length of the SMA actuator with high precision of hundreds μm or less. The state where the SMA actuator is temporarily held denotes that the SMA actuator is in an unstable state. There is, consequently, a problem such that it is difficult to assemble the driving parts.
Further, the shape of the terminal is an essential factor to fix the SMA actuator with high precision. Japanese Patent Application Laid-Open No. 2004-76882 discloses a small terminal capable of retaining an SMA actuator with high precision in a state where the length is adjusted. Japanese Patent Application Laid-Open No. 2004-76882 pays attention only to the terminal but does not suggest adjustment of the distance between a movable member and a fixed member in the SMA actuator.
That is, conventionally, it is difficult to improve the precision of attaching an SMA actuator to a small device due to various errors such as an error in the size of a part and an installation error.